In order to drive compressors, generators, or the like, steam turbines may be used. The steam turbines include a casing and a rotor. The rotor includes a rotating shaft that is rotatably supported by the casing, and turbine blades that are provided integrally with the rotating shaft. At least an output-side end part of the rotating shaft protrudes outward through the casing. In such steam turbines, the rotor is rotated by causing steam fed into the casing from the outside to collide against the turbine blades. A driving target is driven by transmitting the rotation of the rotor to the driving target via the end part of the rotating shaft that protrudes to the outside of the casing.
Steam turbine systems for which such steam turbines are used are provided with a condenser that condenses the steam discharged from a steam turbine, and a ground condenser for discharging the air suctioned into the steam turbine and the steam that leaks to the outside of the steam turbine. In the steam turbine systems, auxiliary steam is used from the outside when the steam turbine, the condenser and the ground condenser are started. Specifically, in the steam turbine, leak of air into the casing is limited when the auxiliary steam is used as seal steam and the inside of the casing is vacuumed. Additionally, in the condenser and the ground condenser, internal air is discharged to the outside by driving an ejector using the auxiliary steam.
Additionally, a steam turbine system described in Patent Document 1 discloses a structure in which the amount of seal steam leaking out of a steam turbine is reduced. Specifically, in the steam turbine system, a seal between a rotating shaft and a casing in the steam turbine has a structure in which a plurality of labyrinth seals and a circumferential direction seal are combined with each other. By adopting such a structure, the amounts of steam and air that leaks out from the seal are reduced.
Meanwhile, even in the steam turbine system as disclosed in Patent Document 1, it is necessary to provide a ground condenser in order to discharge the steam and air that slightly leak from the seal. For that reason, in order to discharge the steam and air within the ground condenser to the outside, it is necessary to supply auxiliary steam to the ground condenser.